A typical internal combustion engine includes a cylinder block through which one or more engine cylinders are machined. The cylinder is typically lined with a cylinder sleeve. A piston is mounted within the cylinder sleeve for reciprocal motion therein. A cylinder head is mounted at one end of the cylinder block. A portion of the bottom surface of the cylinder head combines with the cylinder to form a combustion chamber in a portion of the cylinder between the piston and the cylinder head. A crank case is mounted at the other end of the cylinder block from the cylinder head. The end of the piston opposite the combustion chamber is coupled by a connecting rod to a crank shaft located in the crank case. As the piston is reciprocated in the cylinder by combustion in the combustion chamber, the crank shaft is turned.
The cylinder head has intake and exhaust valves mounted therein which, respectively, allow air and fuel into the combustion chamber prior to combustion and allow combustion byproducts to be exhausted from the combustion chamber following combustion. The intake and exhaust valves are actuated by cams mounted on a cam shaft which is rotated by the rotating crank shaft. The cams are designed to open the valves at precisely the correct instant of piston travel, and hold them open long enough to obtain the most efficient filling and emptying of the cylinder. In many engine designs, the cam activates a pushrod which, in turn, activates a rocker arm in the cylinder head which pushes against the end of a valve stem, thereby opening the valve. The pushrod is coupled to the cam by a cam follower tappet mounted in a tappet block connected to the crank case. The pushrod, rocker arm, and valve are the primary components of the engine valve train in such engine designs.
In many engine designs, such as motorcycle engines, the pushrod extends from a pushrod hole in the tappet block connected to the crank case, runs along the outside of the cylinder block, generally parallel with the cylinder, and enters a pushrod hole in the cylinder head, wherein the end of the pushrod is in contact with the valve rocker arm. Between the tappet block and the cylinder head the pushrod is typically enclosed within a pushrod housing. The pushrod housing is typically mounted at each end thereof in counter bores formed around the pushrod holes in the cylinder head and tappet block. The pushrod housing seals the pushrod holes in the tappet block and cylinder head through which the pushrod passes and forms a chamber through which oil and gasses flow between the crank case and cylinder head to provide oil return and venting through the cylinder head.
For any particular internal combustion engine design, such as a V-twin motorcycle engine, a multitude of crank case designs are possible. For each different crank case design, each pushrod may emerge from a pushrod hole in the tappet block at a different angle with respect to the cylinder head from the pushrod angle of the corresponding pushrod in another crank case design. Thus, the angle and position at which a pushrod enters a pushrod hole in the cylinder head will depend upon the crank case design employed. The angle and position at which the pushrod holes and counter bores for the pushrod housing are machined in the cylinder head will thus depend upon the crank case design with which a particular cylinder head is to be employed.
This creates a challenge for those who manufacture and stock engine parts. In general, a manufacturer or supplier of cylinder heads will be required to manufacture or stock a variety of similar cylinder heads, each having pushrod holes machined therein at slightly different angles. Each such cylinder head is only compatible with a limited number of crank case designs. It is difficult for the manufacturer or supplier to estimate how many of each type of cylinder head to produce or have on hand. If the manufacturer or supplier overestimates the number of cylinder heads of a particular type to be produced or stocked, in order to ensure that customer demands will be satisfied, the cost of producing or stocking the entire cylinder head may be lost, or, at best, there will be a long delay in recovering these costs. Manufacturing and warehousing or stocking a multitude of slightly different cylinder heads can thus be an expensive proposition, the cost of which will be passed on to the ultimate consumer. Failure to have a desired cylinder head on hand, however, can lead to customer dissatisfaction.
Besides increasing the cost of cylinder heads, this problem can also more directly affect consumers. For example, a motorcycle owner may decide to change out the crank case on his motorcycle engine in order to improve engine performance. Typically, the motorcycle owner may also be required to purchase a new cylinder head having pushrod holes machined therein at an angle and in a position which will accommodate the new pushrod angle of the high performance case as well.
A similar problem can occur when a differently designed cylinder head, or other valve train component, is used to replace an existing cylinder head or valve train on an internal combustion engine. Such a changeout may affect the angle and position of the pushrod with respect to the tappet block, thereby requiring replacement of the tappet block with a new tappet block having pushrod holes machined therein at the appropriate angles.
The foregoing problems could largely be avoided if a single cylinder head and/or tappet block design could be fabricated to accommodate a wide variety of pushrod angles and positions.